The present invention relates generally to exposure, and more particularly to an exposure method that is used to fabricate various devices, such as semiconductor chips, display devices, sensing devices and image pick-up devices, and fine contact hole patterns used for micromechanics. Here, the micromechanics is technology for applying the semiconductor IC fabrication technique for fabrications of a fine structure, thereby creating an enhanced mechanical system that may operate at a level of micron.
The photolithography technology for fabricating fine semiconductor devices has conventionally used a projection exposure apparatus that uses a projection optical system to project and transfer a mask (or reticle) pattern onto a wafer. The mask pattern includes a contact. As the critical dimensions of the circuit layout become smaller, it has become more difficult to resolve a fine contact hole stably. A transfer of the pattern with high resolution requires a selection of optimal exposure conditions (such as kinds of masks, illumination condition, etc.) in accordance with kinds of patterns. Moreover, a stabilization of an imaging performance requires a large depth of focus, and the illumination condition affects the depth of focus.
The contact hole pattern includes several kinds, such as a contact hole sequence that periodically arranges contact holes that are adjacent each other and an isolated contact hole that is isolated. A matrix pattern form that arranges a square hole and a checker pattern form that alternately arranges each sequence are known as the contact hole sequence. An actual circuit pattern includes both of the matrix pattern and checker pattern. The illumination condition for the circuit pattern including only the matrix pattern or the circuit pattern including the matrix pattern and checker pattern is already proposed. For example, an annular illumination is suitable for the illumination condition for the circuit pattern including the matrix pattern and checker pattern. The contact hole pattern that has a rectangle form is known. See, for example, Hochul Kim et al., “Layser Specific Illumination Optimization by Monte Carlo Method,” Optical Microlithography XVL, Anthony Yen, Editor, Proceedings of SPIE, Vol. 5040 (2003), pp. 244-250.
A binary mask, a phase shift mask, and an attenuated phase shift mask are known as a kind of mask. The illumination condition includes a polarization condition, a tangential polarization is suitable for a two beam interference, and a radial polarization is suitable for a four beam interference. A polarization control is important technology in the exposure apparatus that includes the projection optical system with high NA, such as an immersion exposure apparatus.
Japanese Patent Applications, Publication Nos. 2000-040656, 2003-203850, 2004-272228 and 2003-318100 are proposed as other conventional technology.
If 0th diffracted light is set as a center of pupil in the projection optical system, checker pattern generates ±1th diffracted light in six directions of around the center of pupil in the projection optical system. Although the two beam interference is effective for the resolution of line, the resolution of contact hole needs three or more beam. If three beam are suitably arranged in the pupil, k1 of Rayleigh equation reduces, the finer is promoted. Here, Rayleigh equation is expressed by the following equation using a resolution R of the projection exposure apparatus, a wavelength λ of a light source, a numerical aperture NA of the projection optical system, and a process constant k1 determined by a development process.R=k1 (λ/NA)  (1)
The checker pattern has a lot of the number of 1th diffracted light that can enter the pupil, and three beam can be easily arranged in the pupil. Therefore, the contact hole pattern that includes only checker pattern will push forward low k1. However, the analysis of optimal exposure conditions for checker pattern including optimal polarization condition for the three beam interference is not fully progressing.